This invention relates generally to the field of interventional medical catheters. More particularly, it relates to catheters used for coronary angioscopy and angioplasty, and similar medical procedures.
An increasingly common procedure for the treatment of atherosclerosis is the method known as Percutaneous Transluminal Coronary Angioplasty, or "PTCA." This procedure employs a long, flexible catheter having a tubular sheath with an internal fluid passage, and a radially expandible and contractible balloon coaxially surrounding the peripheral surface of the distal end of the catheter, in communication with the fluid passage. The catheter is inserted, via a guidewire, into a blood vessel (e.g., a coronary artery) having a localized stenosis, so that the balloon is located at the site of the stenosis. The balloon is inflated, with fluid injected into the passage, to dilate the vessel and relieve the stenosis.
Using this method, the location of the stenosis must first be determined by angiography, which yields only a shadowy, unclear image of the stenosis in one plane. Thus, it is difficult to determine the precise geometry and condition of the stenosis, and the proper positioning of the balloon is not readily confirmed. Consequently, the effectiveness of PTCA treatment is less than optimal, with a significant percentage of treated patients suffering a recurrence of the stenosis.
To overcome this problem, a class of instruments known as fiberscopes has been developed. A state-of-the-art fiberscope is disclosed in U.S. Pat. No. 4,576,145 to Tsuno, et al. The Tsuno, et al. device comprises an elongate flexible tube, the interior of which is divided by a plurality of longitudinally extending partitions into four longitudinal passages or lumens. A first lumen carries a plurality of optical fibers for transmitting illuminating light from an external source. A second lumen carries a light receiving or imaging, optical fiber. A third lumen is an inflation passage for an inflatable elastomeric balloon coaxially surrounding the tube near its distal end. The fourth lumen is for carrying a flushing liquid (such as saline solution) to an outlet at the distal tip of the tube.
A fiberscope of the type described in the Tsuno, et al. patent is used by inserting the distal end into a blood vessel, the interior of which is to be examined for, e.g., a stenosis. The balloon is then inflated with a fluid supplied by an injection device connected to the proximal end of the tube. The inflated balloon substantially reduces the flow rate of blood through the vessel, thereby allowing a relatively small volume of flushing liquid, ejected from the distal tip of the tube, to clear blood away from the area around the tube's tip. Light from the optical transmission fibers can then be used to illuminate this area, with the image of the area being conveyed to an observer by means of the imaging optical fiber.
While the above-described fiberscope provides a clear, detailed view of the area to be observed, the fiberscope must still be removed before most types of therapeutic procedures can be performed. It is possible, of course, to perform laser angioplasty by transmitting laser light through a suitable fiber optic assembly installed in one of the tube's lumens. Indeed, a number of prior art devices have contemplated this expedient, as exemplified in the following U.S. Pat. Nos.: 4,418,688 to Loeb; 4,445,892 to Hussein, et al.; and 4,448,188 to Loeb.
The prior art fiberscopes still suffer from a number of shortcomings. First, to achieve good visual resolution, relatively expensive optical components must be used, thereby making the overall unit too expensive to be disposable. This necessitates costly cleaning and sterilization for reuse. Second, the prior art devices are of a size (diameter) that makes them suitable for use only in larger blood vessels. Third, as previously mentioned, the prior art devices, except in some types of laser angioplasty, must be removed from the patient before therapeutic treatment of the stenosis is undertaken.
In an effort to overcome these disadvantages, there has been devised the concept of incorporating the features of a fiberscope into a balloon angioplasty catheter. This concept is disclosed in European Patent Application No. 85 304962.5, published Apr. 9, 1986 as Publication No. 0177124 in the name of Sumitomo Electric Industries, Ltd. As described therein, this catheter comprises a flexible, tube-like sheath with an expandible angioplasty balloon coaxially surrounding its distal end. The sheath contains a longitudinally-extending light guide for conducting light to the distal end of the catheter, and an imaging optical fiber bundle with suitable imaging lenses at its distal end for transmitting an image from the distal end of the catheter to the proximal end. The interior of the sheath is also provided with an inflation passage for transmitting fluid to inflate the balloon and a flushing liquid passage for conducting a flushing liquid through the catheter and out of an orifice in its distal end.
The device described in the above-identified European Patent Application is disclosed as capable of functioning concurrently as an endoscope to locate and observe a stenosis and an angioplasty device for relieving the stenosis. Thus, this device overcomes some of the above-mentioned limitations of prior art fiberscopes, in that observation and treatment can be performed with one instrument inserted a single time.
Nevertheless, certain drawbacks still exist. Specifically, the above-described device still uses standard optical components (i.e., fiber optics and lenses) thereby necessitating high costs and the requirement of cleaning and sterilization for reuse. Also, although some size reduction is achievable with this design, further size reduction is still desirable.
Thus, there has been established a need for a combined fiberscope/angioplasty catheter that combines good optical qualities with sufficiently low cost so as to be disposable. Further, such a device should be capable of being made in sufficiently small diameters to be usable in smaller blood vessels than has heretofore been possible.